The present invention relates to a method of providing with precision a number of long and narrow through holes in a body made of a high-density material.
Particularly, but not exclusively, the invention relates to the production of an integrated multichannel collimator for use in a device for radiation treatment of a human being or an animal, for instance, ELEKTA AB""s gamma knife.
There are various technical suggestions on how to produce an integrated multichannel collimator and solve the problem of providing many hundreds of geometrically focussing long and narrow conical holes (length of about 200 mm) in a radiation-proof material, such as tungsten, uranium or lead. The narrow through holes or apertures preferably have different size or diameter. It is a technical challenge to produce the length and the small diameter of the conical holes as well as their great number and close spacing with geometric precision. In addition, the materials are difficult to work. In the case of, for instance, sintered tungsten, the largest single pieces which are commercially available weigh about 200 kg, and therefore a massive collimator of 1 tonne is an extremely large dimension challenging the sintering industry.
In the case of a collimator in one single piece, the only existing production alternatives are long-hole boring, spark machining and/or blanks with moulded holes. Boring as well as spark machining are time-consuming and expensive production methods and the required number of long conical holes with said dimensions and strict precision requirements constitute an economically nightmarish problem, which is further aggravated by the risk of rejection in the case of machining errors in an undivided collimator in one piece. Massive sintered tungsten has technical dimensional limitations in commercial production. Uranium has been moulded in single-piece weights of a few tonnes and is the most interesting choice of material from a technical/theoretical point of view, but relatively unknown in non-military production. The alternative production method of precision-moulding holed blanks is also very time-consuming and requires after-treatment, in particular as the long and narrow holes in the dome-shaped collimator build-up expand (converge) from the outside to the inside of the collimator.
An object of the present invention is to provide a method of producing with flexibility and great precision a number of long through holes with an optional, small diameter in a body made of a material which is difficult to machine.
Another object of the invention is to provide a comparatively inexpensive and functional method of producing long, narrow holes in a high-density material.
A further object of the invention is to provide a method which allows production of elongated holes with an optional section in the transverse as well as the longitudinal direction.
According to the invention, these objects are achieved with a method according to the introductory part, which is characterised in that the body is made in the form of a number of partial bodies, which are arranged close to each other and form said body, that each partial body is defined by an outer surface, which is part of the outer surface of the entire body, an inner surface, which is part of the inner surface of the entire body, as well as a pair of boundary surfaces, which extend from the outer surface to the inner surface, that said holes are produced by machining at least one of the boundary surfaces of adjacent partial bodies, each hole extending from the outer surface to the inner surface along said at least one boundary surface, and that the thus machined partial bodies are fixedly attached to each other.
Further developments of the invention will appear from the features stated in the dependent claims.